In such a high-pressure fuel supply system, the fuel is transferred from the low-pressure fuel tank to the high-pressure fuel injection pump by means of the booster pump which operates at low pressure. The pressure of the fuel in the common rail is regulated by means of a PID (proportional, integral, derivative) controller, referred to as the high-pressure fuel injection pump regulator. This controller acts in combination with an actuator fitted to the high-pressure fuel injection pump, which makes it possible to transfer only as much fuel into the common rail as is necessary according to the amount of fuel required by the engine control unit for injection. To achieve this, this actuator includes a valve referred to as a DIV (digital interface valve), which makes it possible to transfer the desired amount of fuel into the common rail, and to return the fuel displaced by the high-pressure fuel injection pump but not desired in the common rail to a return circuit for returning the fuel to the low-pressure tank. The high-pressure fuel injection pump is for example a rotary piston pump that is continuously driven in rotation by the combustion engine. The actuator including a DIV will be referred to hereinafter as the DIV actuator.
The high-pressure fuel injection pump is subject to phasing between the one or more pistons thereof and the pistons of the combustion engine driving it, for example between a top dead center position of a piston of the engine and a top dead center position of a piston of the high-pressure fuel injection pump, so as to make it possible to regulate the exact amount of fuel transferred into the common rail with respect to the position of the crankshaft. The actuator including the DIV is activated by means of an electrical angle-setting command, referred to hereinafter by extension as an angle-setting command for the high-pressure fuel injection pump, produced with respect to a reference angle, i.e. a command issued at a precise angle on an axis of rotation of the high-pressure fuel injection pump, corresponding by construction to a position of the one or more pistons of said pump, so that the valve is closed at a precise position of the one or more pistons of this high-pressure fuel injection pump corresponding to a determined volume of fuel that it is desired to transfer into the common rail. The reference angle is generally set at the top dead center point of the high-pressure fuel injection pump and defined by calibration. The high-pressure fuel injection pump is phased by means of an initial calibration of the reference angle and then by learning this reference angle to account for the assembly and sensor tolerances, in particular in the present case of the high-pressure fuel injection pump and its mechanism of being driven by the combustion engine. If the phasing of the high-pressure fuel injection pump is incorrect, the amount of fuel transferred into the common rail is also incorrect, and consequently so is the pressure established in this rail.
The phasing of the high-pressure fuel injection pump is therefore subject to learning based, in a known manner, on the detection of the integral portion of the PID controller or regulator, in a certain angular window, by varying the theoretical position of the top dead center (TDC) of the high-pressure fuel injection pump. This operation of learning the phasing is performed by the engine control unit.
The electrical-control of the DIV actuator is therefore calibrated so that the electric pulse is positioned at the time of desired closure of the DIV with respect to the position of the one or more pistons of the high-pressure fuel injection pump, so that the amount of fuel determined by the engine control unit is transferred to the common rail. This electrical command of course requires knowledge of the reference angle which is set as explained above. The sequencing of the electrical command is defined during development.
Such an angle-setting command of course requires the synchronization of the engine.
Furthermore, the actuator including the DIV may be activated by means of an electrical timing command, referred to hereinafter by extension as a timing command for the high-pressure fuel injection pump, when the engine has not yet been synchronized, to make it possible to transfer fuel into the common rail before said synchronization, and hence to increase the pressure in this common rail, in particular to accelerate the engine start-up time. This timing signal generally takes the form of a squarewave PWM (pulse width modulation) electrical signal.
The high-pressure fuel injection pump is capable of being driven by an electric drive means with the internal combustion engine, for example the electric starter of the combustion engine.
The above, and in particular the learning, constitutes the elements for checking the operation of a high-pressure fuel supply system, which are known to those skilled in the art.
The maximum amount of fuel that the high-pressure fuel injection pump is able to compress depends on the angle-setting command such as explained above, determined by the regulator for said pump, and applied electrically by the engine control unit.
The performance levels of the regulator for the high-pressure fuel injection pump, of the electrical command for the actuator including the DIV, of the DIV and of said pump themselves are thus linked for the purpose of obtaining the desired result of transferring a precise amount of fuel from the high-pressure fuel injection pump to the common rail.
It is desired that the assembly of the regulator for the high-pressure fuel injection pump and of the electrical command for the actuator including the DIV is able, at any time, to load the high-pressure fuel injection pump to the maximum according to the needs of the engine control unit. There is therefore a need to ensure and to check that this maximum loading is operational. However, the following causes may distort such a check or make it difficult or even impossible:                poor phasing of the high-pressure fuel injection pump during assembly, to such an extent that it cannot be compensated for by learning the phasing;        poor learning of the phasing of the high-pressure fuel injection pump, for example poor learning of the top dead center of said pump;        a fault in the electrical control of the DIV actuator, more specifically in its sequencing, ultimately regarding the actual time at which the DIV is actuated with respect to the time command issued by the regulator for the high-pressure fuel injection pump.        improper calibration of the reference angle for the angle-setting command for the high-pressure fuel injection pump;        abnormal consumption of fuel by the high-pressure fuel supply system leakage.        